This invention relates to deck wrenches used on blasthole drills, and, more particularly, to deck wrench dies for gripping the drill pipe.
Blasthole drills are large machines used to drill holes for explosives in mining operations. A conventional blasthole drill comprises a frame supported by crawlers for movement over the ground, and a mast supported by the frame for movement between a substantially vertical position and a number of angled or non-vertical positions. The mast defines a drill hole axis. A rotary head moves relative to the mast along the drill hole axis. The rotary head engages the upper end of a drill pipe for rotating the drill pipe and driving the drill pipe into the ground. When drilling a blasthole that is deeper than the height of the mast, more than one section of drill pipe must be used. After the first section of drill pipe is driven into the ground, the rotary head moves back to the top of the mast and another section of drill pipe is connected to the top of the first section. The rotary pipe then drives the second section into the ground. It is not unusual to use four sections of drill pipe. Such a deep blasthole is referred to as a “multi-pass” blasthole.
After drilling a multi-pass blasthole, it can be difficult to break the joint between two pipe sections. A blasthole drill typically includes an automatic breakout wrench for breaking a joint if the rotary head cannot do so. An automatic breakout wrench is disclosed in U.S. Pat. No. 4,128,135. The automatic breakout wrench turns the upper pipe section while the lower pipe section is held by deck wrenches.
A conventional breakout wrench includes a swing arm pivotable relative to the mast between extended and retracted positions. A wrench member pivots relative to the swing arm about the drill hole axis when the swing arm is in the extended position. The wrench member carries dies for gripping the pipe section. A clamping jaw pivots relative to the wrench, member between a clamping position and a non-clamping position. The jaw also carries a die for gripping the pipe section. When the swing arm is in the extended position, movement of the jaw to the clamping position causes the pipe section to be gripped by the dies on the jaw and on the wrench member. Thereafter, pivotal movement of the wrench member relative to the swing arm (the clamping jaw moves with the wrench member) turns the pipe section to break the joint. Pivotal movement of the wrench member is caused by a hydraulic breakout cylinder connected between the swing arm and the wrench member.
In U.S. Pat. No. 5,653,297, shims allow for adjustment of the dies to compensate for pipe wear and to accommodate different pipe sizes. More particularly, the pipe section is gripped by two dies mounted on the wrench member and by one die mounted on the clamping jaw. Each die is held in place by upper and lower fasteners. Shims can be inserted behind each die to adjust the position of the die. Each shim has therein an aperture through which the upper fastener extends to hold the shim in place. The bottom of each shim has therein an upwardly extending slot through which the lower fastener extends. The shim is removed by loosening the lower fastener and by removing the upper fastener from the shim aperture. The slot in the shim allows upward movement of the shim relative to the lower fastener, while the lower fastener maintains the position of the shim.
Two problems occur with current break out wrenches. One is that when a drill pipe wears from the abrasion of bailing rock from the hole, a reduction in pipe diameter occurs, and the amount of reduction varies and is greater near the bottom of the pipe, because the bottom of the pipe is in the hole longer, than near the top of the pipe. This results in a tapering of the pipe known as penciling. The current wrench dies do not accommodate tapered pipe, so the die does not make proper contact with the pipe and hence has difficulty gripping the worn pipe. The second problem is that current wrenches require shims to be added to the wrench as the pipe diameter reduces from wear. Typically, this is not done by the mine due to a lack of knowledge or desire to manually bolt in the shims. As a result, the wrench slips on the pipe.